Flame front location method



May 1, 1962 H. w. PARKER FLAME FRONT LOCATION METHOD Filed July 27, 1959 INVENTOR. H.W. PARKER www??? 3,031,762 FLAME FRNT LOCA'IIQN METHD Harry W. Parker, Bartlesville, Siria., assigner to Phiilips Petroleum Company, a corporation of Delaware Filed duly 2'7, 1959, Ser. No. 829,908 9 Claims. {CL 331-1) This invention relates to a method of determining the location and pattern of a combustion or dame front being advanced thru a subterranean combustible carbonaceous stratum by in situ combustion techniques.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein followed by injection of air thru the ignition borehole and recovery of product hydrocarbons and combustion gas thru another borehole in the stratum is a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum usually plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difficulty and to permit the continued progress of the combustion zone thru the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

In situ combustion techniques are being applied to tar sands, shale, Athabasca sand and other strata in virgin state, to coal veins by fracturing, and to strata partially depleted by primary and even secondary and tertiary recovery methods.

When producing a stratum by in situ combustion, it is desirable to know the progress of the combustion front as it is advanced from well to well in order to determine the changes in operation conditions which are desirable to produce more uniform movement or more rapid Inovement of the front in certain areas. It is also desirable to know what sections of a well pattern have been produced or burned at any stage of the in situ combustion operation. Heretofore combustion front movement has been determined by drilling temperature-sensing holes into the stratum being produced and placing in these holes thermocouples or other temperature-sensing devices which indica-te a sharp rise in temperature as the flame front arrives at the locus of the temperature-sensing device. One disadvantage in this method lies in the fact that lthe extremely high temperatures of the combustion front frequently destroy the temperature-sensing apparatus. Another disadvantage is in the cost of drilling holes to the formation level. This invention is concerned with a nethod of determining the progress and pattern of a combustion front in a carbonaceous stratum which avoids the aforesaid diiculties.

Accordingly, the principal object of the invention is to provide a method of determining the location and pattern of a combustion front as it is moved thru a combustible carbonaceous stratum from an ignition well to an offset well, which method is simple and economical to use. Another object is to provide ra method of determining the progress of a combustion front thru a stratum which is 'icc substantially immediately responsive to the movement of the combustion front. Other objects of the invention will become apparent upon consideration of the accom panying disclosure.

A broad aspect of the invention comprises periodically measuring the elevation of the ground at one or more points directly above the path of a combustion front until the ground at said point rises, thereby indicating the arrival of the combustion front directly under said point. The invention is based upon the discovery that combustion of the carbonaceous stratum causes an expansion of the stratum which is substantially immediately translated to a rise in the elevation of the ground surface directly over the expanded stratum.

To illustrate the invention, a series of surface level profiles were made along a radius from an ignition well in the Bellamy, Missouri, tar sand in a radial drive 9-spot well pattern in which 9 wells were positioned in a ring concentric with a central ignition well. tIt was found that a surface displacement of 0.09 foot was observed at the time the tire front had reached its maximum extent. About 0.04 to 0.05 foot of this maximum rise was recovered 18 days after the combustion was terminated and the formation temperatures had been reduced to within 30 of their original value by water flooding. The maximum increase in elevation was more than could be accounted for by thermal expansion of the combustion zone. This, plus the fact that the increase was not entirely re coverable upon cooling, suggests that a major part of the expansion may have been Caused by rock decomposition and fracturing.

The Bellamy tar sand used in the test was only 6 feet thick and under 55 feet of overburden. In a thicker stratum, the rise in elevation of the ground surface above the combustion zone would be proportionately increased so that this rise in elevation offers a readily measurable and reliable effect of the combustion zone which makes it possible to follow the advance of the zone thru the stratum and plot the pattern ofthe combustion zone from time to time. For a stratum feet in thickness, surface elevation increases of the order of a foot or more will result even at depths considerably greater than the 55 feet of depth of the Bellamy tar sand.

In determining the surface level profiles at the Bellamy test site a iixed level line of sight was maintained over a series of iron pipes cemented in bedrock at a depth of l5 feet and extending to above ground level. These test points were located on a radius from the ignition well at distances of 3, 15, 30, and 45 feet therefrom. Level rod readings were made at the 4 points periodically to sense any rise in the evel of these points. It was found that there was a delinite measurable rise in the surface level at each point, the maximum being 0.09 foot.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which FIGURE 1 is a plan View of a lring-type well pattern and elevation measuring points in a desirable pattern thereon; and FIGURE 2 is a similar plan view of a line-drive well pattern.

Referring to FIGURE l, a central well 10 is positioned in a carbonaceous stratum 11 and is ringed by wells 12 in a substantially symmetrical pattern. A ring 14 of test elevation points X is 4concentric with well 10 and also with ring of wells 12. A second concentric ring 16 of test elevation points X is positioned intermediate the first ring and the ring of wells. There is an observation o1' test point X on each radius connecting the central well with a well in the ring. Extra test points are positioned in the outer ring of test points. The pattern of test points shown in FIGURE 1 is preferred but other test patterns are within the scope of the invention.

In FIGURE 2, a line of ignition wells 20 is flanked on one side by a parallel line of wells 22 and on the other side by a second parallel line of wells 24. Two lines of test points 26 and 28 are positioned intermediate line of wells 2t) and line of wells 24. The test points in lines 26 and 2S also lie on lines connecting each ignition well with the opposite Well in the parallel line of wells 22. A similar pattern of test points is located on parallel lines 30 and 32 intermediate the ignition Wells and line of wells 24.

In producing the stratum with the well pattern of FIGURE 1-, it is conventional to ignite vthe stratum around ignition well and either drive the combustion front to wells 12 in the ring by injecting air or other combustion supporting gas thru well 1i), or by injecting the air thru wells 12so as to advance the front inversely to the flow of air.

In utilizing the well pattern shown in FIGURE 2, according to one method, ignition of the stratum around alternate wells 26 is effected and the front around each ignited well is driven to the adjacent wells so as to estabm lish a line combustion -front extending along each side of line of wells 20. Air is then injected thru wells 22 and 24 so as to move each line combustion front inversely to the injected air toward adjacent'line of wells 22 or 24. Of course, it is also feasible to inject the combustion-suplporting gas thru Wells 20, so as to drive the combustion fronts by direct drive toward wells 22 and 24, in applications where the stratum is not subject to plugging by driving heavy liqueed hydrocarbons into the cool stratum ahead of the combustion front. During inverse drive, ignition wells 2t) serve as production wells, while with direct drive, wells 22 and 24 are production wells. In the ring-type pattern of FIGURE 1, utilizing inverse air injection, production is recovered thru well 10 and with direct drive production is recovered thru wells 12.

Elevation testv points may be provided by driving iron stakes or pipe into the ground a few feet. Any object iirmly fixed to the earth at ground level will suiice for an elevation test point. The elevation of the various test points may be the same or it may vary from point to point. It is the change in elevation relative to a ixed level that provides the needed measurement to determine movement of the combustion zone.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

l. In a process wherein a combustion front is being driven thru a subterranean combustible carbonaceous stratum, the method of determining the progress of said front which comprises periodically measuring the relative elevation of the ground at at least one point directly above the path of said front until said point rises, thereby indicating the arrival of said front directly under said point.

2. In a process wherein a combustion front is being advanced thru a subterranean combustible carbonaceous stratum, the method of determining the advance of said front which comprises measuring the relative elevation of theground at a point directly over the path of said iront before said front arrives directly below said point; and periodically measuring the relative elevation of said point until a rise in elevation is detected, thereby indicating the arrival of s aid front directly under said point.

3. The method of claim 2 wherein the elevation of said point is measured in relation to a fixed horizontal line above ground surface.

4. The method of claim 2 wherein said front is being driven thru said stratum from an ignition well to an offset well therein and said point is on a line between the wells; :and including the steps of measuring the relative elevation of the ground at other points on said line before said front .arrives directly below said points; and periodically measuring the relative elevation of said points until a rise in elevation is detected at each point, thereby determining fthe progress of said front between said wells.

5. A method of determining the progress of a comlbustion 'front moving away from an ignition borehole in n subterranean combustible carbonaceous stratum which comprises periodically measuring the relative elevation of theV ground at spaced points along the path of said front von a radius from said well until a rise in elevation occurs at each successive point away `from said well, whereby the progress of said front is determined.

6. A method of determining the progress and pattern of a combustion front being advanced thru a subterranean combustible carbonaceous stratum from a central ignition well to a ring of surrounding wells which comprises periodically measuring the elevation of the ground at a iirst series of points symmetrically spaced on a rst circle concentric with said ignition well and between said well and said ring of wells until a rise in elevation occurs at each point; and periodically measuring the elevation of the ground at a second series of points symmetrically spaced on a second concentric circle intermediate said iirst circle and said ring of wells until a rise in elevation occurs, whereby the progress and pattern of said combustion front is determined.

7. The method of clair-n 6 wherein there is a point in each ring on each radius between said ignition well and each of the Wells of the ring.

8. A method of determining the progress and pattern of a combustion front being advanced thru a subterranean combustible carbonaceous stratum from a line of ignition wells toward a second line of wells which comprises periodically measuring the elevation of the ground at spaced points in a iirst line parallel with said line of ignition wells and intermediate the lines of wells until a rise in elevation occurs at each point; and periodically measuring the elevation of the ground at spaced points in a second parallel line intermediate said iirst line and said second line of wells until a rise in elevation occurs at each point, whereby the progress and pattern of the combustion front is determined.

9. The method claim 8 wherein there is a point in each said iirst and second lines directly opposite each ignition well.

References Cited in the iile of this patent UNITED STATES PATENTS 1,441,153 Jefferson Ian. 2, 1923 2,025,719 Blau et al. Dec. 3l, 1935 2,616,177 Bazhaw Nov. 4, 1952 2,770,305 Pirson Nov. 13, 1956 2,793,696 Morse May 28, 1957 2,803,305 Behning et al Aug. 20, 1957 2,888,987 Parker June 2, 1959 

